114 lines
3.2 KiB
Plaintext
114 lines
3.2 KiB
Plaintext
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include::meta/VK_NV_corner_sampled_image.txt[]
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*Last Modified Date*::
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2018-08-13
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*Contributors*::
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- Jeff Bolz, NVIDIA
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- Pat Brown, NVIDIA
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- Chris Lentini, NVIDIA
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This extension adds support for a new image organization, which this
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extension refers to as "corner-sampled" images.
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A corner-sampled image differs from a conventional image in the following
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ways:
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* Texels are centered on integer coordinates.
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See <<textures-unnormalized-to-integer, Unnormalized Texel Coordinate
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Operations>>
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* Normalized coordinates are scaled using [eq]#coord * (dim - 1)# rather
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than [eq]#coord * dim#, where dim is the size of one dimension of the
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image.
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See <<textures-normalized-to-unnormalized, normalized texel coordinate
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transform>>.
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* Partial derivatives are scaled using [eq]#coord * (dim - 1)# rather than
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[eq]#coord * dim#.
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See <<textures-scale-factor,Scale Factor Operation>>.
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* Calculation of the next higher lod size goes according to
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[eq]#{lceil}dim / 2{rceil}# rather than [eq]#{lfloor}dim / 2{rfloor}#.
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See <<resources-image-miplevel-sizing,Image Miplevel Sizing>>.
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* The minimum level size is 2x2 for 2D images and 2x2x2 for 3D images.
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See <<resources-image-miplevel-sizing,Image Miplevel Sizing>>.
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This image organization is designed to facilitate a system like Ptex with
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separate textures for each face of a subdivision or polygon mesh.
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Placing sample locations at pixel corners allows applications to maintain
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continuity between adjacent patches by duplicating values along shared
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edges.
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Additionally, using the modified mipmapping logic along with texture
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dimensions of the form [eq]#2^n^+1# allows continuity across shared edges
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even if the adjacent patches use different level-of-detail values.
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=== New Object Types
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None.
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=== New Enum Constants
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* Extending elink:VkImageCreateFlagBits
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** ename:VK_IMAGE_CREATE_CORNER_SAMPLED_BIT_NV
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=== New Enums
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None.
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=== New Structures
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* elink:VkPhysicalDeviceCornerSampledImageFeaturesNV
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=== New Functions
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None.
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=== New Built-In Variables
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None.
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=== New SPIR-V Capabilities
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None.
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=== Issues
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. What should this extension be named?
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+
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--
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DISCUSSION: While naming this extension, we chose the most distinctive
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aspect of the image organization and referred to such images as
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"corner-sampled images".
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As a result, we decided to name the extension NV_corner_sampled_image.
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--
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. Do we need a format feature flag so formats can advertise if they support corner-sampling?
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+
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--
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DISCUSSION: Currently NVIDIA supports this for all 2D and 3D formats, but
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not for cubemaps or depth-stencil formats.
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A format feature might be useful if other vendors would only support this on
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some formats.
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--
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. Do integer texel coordinates have a different range for corner-sampled images?
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+
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--
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RESOLVED: No, these are unchanged.
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--
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. Do unnormalized sampler coordinates work with corner-sampled images? Are there any functional differences?
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+
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--
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RESOLVED: Yes they work.
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Unnormalized coordinates are treated as already scaled for corner-sample
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usage.
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--
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. Should we have a diagram in the "Image Operations" chapter demonstrating different texel sampling locations?
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+
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--
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UNRESOLVED: Probaby, but later.
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--
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=== Version History
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* Revision 1, 2018-08-14 (Daniel Koch)
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- Internal revisions
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